A Tribune investigation of hundreds of earnings disclosures before formal announcements of results in the first nine months of this year - and the nearly 2,700 stock trades preceding them - discovered that insider sales accelerate before warnings, usually with profitable results.

Executives and directors invariably say they had no significant, private information when they traded. Otherwise, they would be breaking the law.

But the issue, experts say, is familiar: What did they know, and when did they know it?

Insiders clearly know more than the everyday investor, but that doesn't necessarily make trades illegal. Authorities have not filed insider-trading charges in any of these cases.

But the sheer volume of trades - some just days before the warnings - and the stark outcomes suggest the timing can be more than coincidental.

"A lot of them know it" before the news is announced, said author and Wall Street expert Donald Christensen, a longtime editor of a newsletter that followed insider transactions.

"The direct relationship between the selling and the event, though - it's very hard to prove what they knew."

Earnings pre-announcements, especially about operating results, can provoke large movements in share prices.

The Tribune investigation found stock price reactions differed sharply after sales and purchases, and insiders' trades were frequently uncanny.

In general, after insiders sold, the warning pummeled the stock. After purchases, however, even when traders digested the warning, the stock was usually higher.

Dozens of insiders, for example, sold in the two weeks before they predicted a shortfall in operating results. Afterward, those firms' shares fell sharply overall - an average of 6.7 percent from the day before the news to the next day's close and 7.4 percent from the insiders' sale price.

The result: Insiders saved millions of dollars they would have lost by waiting.

Insiders purchased stock before that kind of announcement only eight times in the nine months. But when they did, the reaction was very different: Those firms' shares fell an average of only 1.5 percent just after it, and actually averaged 1.6 percent above the insiders' purchase price.

Sales within two weeks before any earnings warning, including a one-time item lowering results, totaled $1.3 billion. Insiders sold $316 in stock for every $1 they purchased, dwarfing the 22-to-1 ratio for the overall market calculated by Thomson First Call.

Excluding a $1.2 billion preplanned sale in late May by Microsoft chief executive Steven A. Ballmer just days before the software maker announced it would pay $750 million in a litigation settlement, the sell-buy ratio still exceeded the overall market's.

A spokeswoman declined to discuss details of Ballmer's sale.

Officials can be immune to insider-trading charges by setting and sticking to a planned schedule of transactions.

It's unknown how many of the trades the Tribune studied were scheduled in advance, but firms acknowledged many were not.

And even when they are planned, firms can wait to issue warnings after the sale; insiders only have to show they had no private, important information when they planned them.

"High-level executives have tremendous discretion over the timing and content of corporate disclosures," said insider-trading expert Donna Nagy, a professor at the University of Cincinnati law school.

"Insiders with pre-existing trading plans may well be tempted to delay disclosure so that a preplanned trade can be executed at the best possible price," she said.

Some top executives, meanwhile, said any stock sales by chief executives are dicey.

"There's never a time when I don't have inside information" as a CEO, said William W. George, a recognized corporate governance expert and former head of Medtronic Inc., a medical technology firm in Minneapolis. "That's my job."

Experts said more executives are keeping their shares amid the uproar over executive pay.

Michael H. Jordan, CEO of Electronic Data Systems Corp. in Plano, Texas, and a director at several companies in his career, said officials should link their rewards to firms' results over the long haul.

"I doubt that I would sell any shares while I was active," he said.

At Alpharma Inc., a specialty pharmaceutical company in Fort Lee, N.J., three executives - Vice President Marie Amerasinghe, division President Carolyn Wrenn and Treasurer Albert N. Marchio II - sold nearly $350,000 in stock Aug. 25-27. Those have been their only reported sales this year.

On Sept. 8, blaming weakness in August sales as a key factor, the firm said quarterly earnings would be 10 to 15 cents a share, barely half of previous estimates. Shares fell more than 20 percent in two days of trading. The stock spent most of the next three months below their sale prices, even as the market rallied.